1. Field of the Invention
The present invention relates to ink jet printing devices, and more particularly, to a vibration damping mechanism associated with the orifice plate in the printing head in which traveling waves are used to generate uniform filaments and droplets from the orifices.
2. Prior Art
In an ink jet printing device of the general type to which the present invention relates, it is common to use some means of substantially reducing, if not eliminating, reflected wave propogation through the orifice plate when it is stimulated at high frequency so as to vibrate along its length. For example, the device disclosed in Lyon et al U.S. Pat. No. 3,739,393 utilizes a traveling wave stimulation technique and in order to dampen out interferring reflected waves polyurethane or other similar material is placed in contact with the end portions of the orifice plate in order to dampen out vibrations remote from the point of contact of the mechanical stimulator. Such devices, although they are fairly efficient in damping out reflected waves at the ends of the orifice plate, suffer from several deficiencies.
One difficulty associated with the use of such plastic or rubber like bumpers is that since they are contained within the ink reservoir above the orifice plate they produce a source of contamination for the ink supply which results in small particles becoming lodged in the extremely small orifices, thus clogging the orifices. In addition, it is believed that a significant boundary effect occurs at the leading edge of the tapered dampers in the case where such dampers are poured in position as is disclosed in the Lyon et al patent. These boundary effects result in generation of interfering waves which propagate along the orifice plate and are detrimental to propagation of the main wave being generated.
Further, the wedge of material in each end of the orifice plate assembly is intended to provide a gradual change in characteristic impedence of the orifice plate while simultaneously adding a high damping component. However, as a practical matter, the dampers are less effective than is desirable due to the impedence mismatch between the orifice plate and the polyurethane dampers.